Fibre optics sensors may be used for measuring many parameters such as temperature, strain, pressure, displacement, electric field, refractive index, rotation, position and vibration. However because of sensitivity to these parameters, a fibre optic sensor can often suffer from cross sensitivity so that if used for measuring one parameter it may well also be effected by one or more of the other parameters. Although some of the cross sensitivity can be designed out of such sensors, it has proved particularly difficult to eliminate strain-temperature cross sensitivity.